1 Oligocene ramp system (Asmari Formation) in the west of Fars province: Microfacies and sedimentary environment Samir Akhzari *1 , Ali Seyrafian 2 , Hossein Vaziri-Moghaddam 3 *1 University of Isfahan, Faculty of Sciences, Department of Geology; E-mail: samir.akhzari@gmail.com 2 University of Isfahan, Faculty of Sciences, Department of Geology; E-mail: Seyrafian_ali@hotmail.com 3 University of Isfahan, Faculty of Sciences, Department of Geology; E-mail: avaziri7304@gmail.com Abstract In this paper, microfacies and sedimentary environment of the Asmari Formation are investigated at the northwest of Deris village, located at 7 km northwest of Kazerun city (west of Fars province). The Asmari Formation in this section consists of 460 m massive, thick, medium and thin bedded gray and cream to gray limestone, slightly dolomitic with interbeds nodular and marly limestone. More than 270 thin sections from this Oligocene carbonate interval have been prepared, studied and analyzed. Facies analysis on the basis of depositional texture, benthic foraminifera and non-foraminifera caused to distinguish 14 microfacies and 4 subfacies: O1- Bioclastic nummulitidae floatstone-rudstone, O1-1- Bioclastic nummulitidae echinoids floatstone-rudstone, O2- Bioclastic lepidocyclinidae nummulitidae Neorotalia rudstone, O3- Bioclastic nummulitidae Neorotalia packstone-rudstone, O3-1- Bioclastic nummulitidae Neorotalia corallinacean packstone- rudstone, O4- Bioclastic lepidocyclinidae Neorotalia packstone, O4-1- Bioclastic lepidocyclinidae Neorotalia corallinacean packstone, O5- Bioclastic Neorotalia corallinacean packstone, O6- Bioclastic coral corallinacean Neorotalia packstone-rudstone, Sh- Neorotalia corallinacean echinoids packstone- grainstone, L1- Coral benthic foraminifera floatstone- rudstone, L2- Benthic foraminifera (perforate and imperforate) peloidal packstone, L3- Bioclastic imperforate foraminifera corallinacean packstone, L4- High diversity imperforate foraminifera bioclastic packstone-grainstone, L5- Bioclastic miliolids wackestone-packstone, L5-1- Bioclastic miliolids Valvulinid wackestone-packstone, L6- Small rotaliids Discorbis bioclastic wackestone, and T- Sandy mudstone. Based on these facies association lagoon and open marine environments related to inner and middle parts of a homoclinal ramp have been considered for deposition of the Asmari Formation. Middle ramp fauna are mostly characterized by hyaline benthic foraminifera specially nummulitidae and lepidocyclinidae, and inner ramp is dominated by imperforate foraminifera. Keywords: Asmari Formation, Oligocene, Microfacies, Sedimentary environment, Homoclinal ramp. Introduction The Asmari Formation, a thick carbonate sequence of the Oligocene-Miocene, is present in the most of the Zagros basin, consists of limestone, dolomite limestone, dolomite and marly limestone [1]. The most recent studies of the Asmari Formation are on biostratigraphic criteria [2 and 3], microfacies and depositional environment [4] and depositional environment and sequence stratigraphy [5 and 6]. Regional setting Iran territory stands in middle part of Alp-Hymalia folded belt [7] "Figure 1". Based on sedimentary sequences, magmatism and metamorphism and structural setting, the Iranian plateau consists of eight continental fragments, including sanandaj-Syrjan, Urumieh-Dokhtar, Central Iran, Alborz, Kopeh-Dagh, Lut, Makran and Zagros [8] "Figure 2". The study section is located in the Zagros basin. The Zagros basin is located to the southwest of Iran and consists of a thick sediment deposits that covers the Precamberian basement formed during the Pan-Africa orogeny [9]. It is divided into six major tectonostratigraphic regions: the interior and coastal Fars province, Dezful embayment, the Izeh zone, the Lurestan province and the high Zagros zone [10 and 11] "Figure 3".